German Published Pat. Specification No. 2,016,223 describes the manufacture of polymeric products which can be diluted with water and which consist of 10 - 70 % by weight of an unsaturated fatty acid ester, 85 - 10 % by weight of polybutadiene and 5 - 20 % by weight of maleic anhydride. On page 4, last paragraph, of this German Published Patent Specification it is stated that the manufacturing process is carried out by first reacting the unsaturated fatty acid ester and the polybutadiene with one another at 180.degree.- 270.degree.C. and then forming the adduct of maleic anhydride. The binders thus obtained are stated to give electrophoretically deposited films which after stoving have improved corrosion protection, better permanent elasticity and good hardness. The bath solutions are stated to have excellent storage stability and the binder is supposed to be capable of trouble-free deposition even at high potentials. However, the binders obtained according to German Published Patent Specification 2,016,223 suffer from a series of disadvantages. Thus, the electrophoresis baths prepared with these binders display only inadequate values of the throwing power, and on stoving, especially in the case of fairly thick layers (above 24 .mu.), the films show insufficient hardening in depth and the electrophoretically deposited films show marks from drops of water after having been sprayed down with water and then stoved.
These disadvantages are overcome by the synthetic resins manufactured according to the process of the invention. The synthetic resins obtained according to this process display good to excellent values of the throwing power when used as binders in electrophoretic coating baths. The electrophoretically deposited films cure well in depth, on stoving at about 180.degree.C for 30 minutes, even in the case of thick layers (23.degree. - 28 .mu.). The electrophoretically deposited films can be sprayed down with water and the films show no marks from drops of water after stoving.
British Pat. Specification No. 1,102,652 describes the manufacture of water-soluble binders suitable for the electrophoretic coating process, polybutadiene being reacted with maleic anhydride. These electrophoresis baths prepared with such binders, however, display inadequate values of the throwing power. The films show inadequate hardness after stoving.
British Patent Specification No. 1,154,174 describes the manufacture of binders which can be diluted with water and are suitable for the electrophoretic coating process, and which consist of 40 - 80 % by weight of polybutadiene, 15 - 55 % by weight of unsaturated fatty acid and 5- 15 % by weight of fumaric acid. Page 2, lines 38 - 43 of this Patent Specification mentions that hydrocarbon resins based on cyclopentadiene or piperylene can also be added. These binders also show poor values of the throwing power in electrophoresis baths. After spraying down with water and stoving, the films obtained show marks from drops of water and more inadequately hardened in depth.